This invention relates to a record position measuring apparatus for evaluating the quality of the record (printout) of a printer or the like and, more particularly, to a record position measuring apparatus for measuring an amount of the displacement of the recorded position of the basic colors such as yellow, magenta, cyan, etc.
FIG. 1 is a perspective view illustrating a conventional record position measuring apparatus disclosed in Japanese Patent Laid-Open No. 60-242343, for example. In FIG. 1, the reference numeral 1 designates a planer bed, 2 is a substantially U-shaped gate mounted on the bed 1 so as to bridge over the central portion of the bed 1, 3 is a moving mechanism mounted on the upper portion of the gate 2, 4 is a He-Ne laser device mounted to the moving mechanism 3, 5 is a unit attached to one end face of the He-Ne laser device 4, 6 is a controller connected to the bed 1, 7 is a computer connected to the controller 6, 8 is a monitor connected to the computer 7, 9 is a printer connected to the computer 7, and 10 is a printing paper mounted on the bed 1 and on which a test pattern is printed.
FIG. 2 is a front view schematically illustrating the interior of the unit 5 shown in FIG. 1. In FIG. 2, 5a, 5b and 5c are lenses, and 5d is a photoelectric conversion element. The character L designates laser beam.
The operation of the conventional apparatus as above described will now be described in conjunction with FIG. 3, which is a plan view showing a printing paper 10 on which a test pattern is printed.
First, the printing paper 10 on which the test pattern shown in FIG. 3 is placed on the bed 1, and the density of the printing paper 10 is measured while the bed 1 is being moved in the Y-direction by an unillustrated mechanism. When the laser beam crosses the line of the cross pattern 10a which extends in the X-axis, its position is detected. Then, the He-Ne laser apparatus 4 and the unit 5 are moved into the X-direction by the moving mechanism 3 to detect the position of the line of the pattern 10a extending in the Y-axis.
That is, the laser beam L emitted from the He-Ne laser apparatus 4 is irradiated onto the printing paper 10 through the lenses 5a and 5b. Then, the light reflected at the printing paper 10 is collected on the photoelectric transducer element 5d by the lens 5c, whereby the information on the reflected light (the positional information of the cross pattern 10a) is collected through the control apparatus 6 on the controller 6.
Thus, by obtaining the position of the crossing point of the cross pattern 10a and comparing it with a reference position, the displacement of the printed position of the cross pattern 10a can be measured. When neccessary, the measured amount of the displacement can be output on the monitor 8 and the printer 9.
In the record position measuring apparatus described above, when it is desired to measure the amount of the displacement or misalignment of each basic color such as yellow, magenta, and cyan, etc. printed on the printing paper by a color printer, the problems which will be discussed below arise.
Firstly, since the He-Ne laser apparatus is used as an irradiation light souce, the density change of the test pattern of a particular color cannot be measured by the photoelectric transducer element 5d. In particular, since the He-Ne laser apparatus which emits a red laser light is used, it is impossible to achieve density measurement as to magenta or red.
Secondly, since the laser beam L scanns in the X-and Y-directions, the bed 1 and the moving mechanism 3 must be driven respectively in each direction for determining a single record position, requiring relatively long time for processing.
Thirdly, the boundaries between the ink and the paper at which the density abruptly changes, are curved within a width of about 50 .mu.m because of the rough paper surface and the fibers and cavities of the paper. Therefore, with the system in which the laser beam L sequentially scans in the X- and Y-directions, only a localized pattern position can be measured, resulting in a large error in the pattern position. While the measuring accuracy can be improved by measuring the density changing position at a plurality of measuring points and statistically processing the measured data, this measure needs relatively long time for driving the bed 1 and the moving mechanism rendering it practically impossible to use.